Liquid dairy products, such as milk, are generally thermally processed to increase their stability and to render them microbiologically safe. Unfortunately, thermally treating of milk can result in color changes, gelation, and the formation of off-flavor notes in some instances. For example, lactose in milk heated to high temperatures can interact with proteins and result in an unsightly brown color. This undesired condition is often referred to as browning or a browning or a Mallaird reaction. Gelation, on the other hand, is not completely understood, but the literature suggests that gels may form, under certain conditions, as a three-dimensional protein matrix formed by the whey proteins. See, e.g., Datta et al., “Age Gelation of UHT Milk—A Review,” Trans. IChemE, Vol. 79, Part C, 197-210 (2001). Both gelation and browning are generally undesirable in milk since they impart objectionable organoleptic properties.
The concentration of milk is often desired because it allows for smaller quantities to be stored and transported, thereby resulting in decreased storage and shipping costs, and may allow for the packaging and use of milk in more efficient ways. However, the production of an organoleptically-pleasing, highly concentrated milk can be difficult, because the concentration of milk generates even more pronounced problems with gelation, browning, and also the formation of compounds imparting undesired flavor and off-notes. For instance, milk that has been concentrated at least three fold (3×) has an even greater tendency to undergo protein gelation and browning during its thermal processing. Additionally, due to such high levels of protein in the concentrated milk, it may also have a greater tendency to separate and form gels over time as the product ages, thereby limiting the usable shelf life of the product.
A typical method of producing concentrated milk involves multiple heating steps in combination with the concentration of the milk. For example, one general method used to produce concentrated milk involves first standardizing the milk to a desired ratio of solids to fat and then forewarming the milk to reduce the risk of the milk casein from coagulating during later sterilization. Forewarming also decreases the risk of coagulation taking place during storage prior to sterilization and may further decrease the initial microbial load. The forewarmed milk is then concentrated to the desired concentration. The milk may be homogenized, cooled, restandardized, and packaged. In addition, a stabilizer salt may be added to help reduce the risk of coagulation of the milk that may occur at high temperatures or during storage. Either before or after packaging, the product is sterilized. Sterilization usually involves either relatively low temperatures for relatively long periods of time (for example, about 90° C. to about 120° C. for about 5 to about 30 minutes) or relatively high temperatures for relatively short periods of time (for example, about 135° C. or higher for a few seconds). Processes to concentrate milk generally report shelf stability ranging from about 1 month to greater than about 6 months.
Various prior approaches for the production of concentrated milk have been documented that report the formation of dairy concentrates having varying levels of stability. For example, U.S. Patent Publication Number 2003/0054079 A1 (Mar. 20, 2003) to Reaves discloses a method of producing an ultra-high temperature milk concentrate generally having 30 to 45 percent nonfat milk solids. That is, Reaves discloses a milk concentrate generally having 11 to 17 percent protein and 16 to 24 percent lactose (assuming nonfat milk solids are about 37 percent protein and about 54 percent lactose). Reaves notes that such nonfat dairy solid levels are critical to the process and that lower nonfat milk solids will not produce acceptable results. Reaves reports shelf lives of 30 days to 6 months for the resulting milk concentrate. With such high lactose levels, it is expected that the concentrated milks of Reaves will undergo browning or Mallaird reactions during sterilization resulting in an undesired brownish color.
Reaves also discloses the preheating of milk for 10 minutes at 65° C. (150° F.) to produce a preheated, milk starting product. The milk starting product is then pasteurized at 82° C. (180° F.) for 16 to 22 seconds and evaporated under elevated pasteurizing temperatures (i.e., 10 minutes at 62° C. (145° F.) under vacuum) to produce an intermediate, condensed liquid milk. The evaporation process used by Reaves will result in a condensed milk having the same relative amounts of protein and lactose as in the starting milk source. A cream and stabilizer, such as sodium hexametaphosphate or carrageenan, are then added to the intermediate milk, which is then ultrapasteurized in two stages wherein the first stage is at 82° C. (180° F.) for 30 to 36 seconds and second stage is at 143° C. (290° F.) for 4 seconds. The ultrapasteurized beverage is then homogenized after the pasteurization and packaged to form the ultrapasteurized liquid milk concentrate.
U.S. Patent Publication Number 2007/0172548 A1 (Jul. 26, 2007) to Cale discloses a process of producing a concentrated milk with high levels of dairy proteins and low levels of lactose. The process of Cale discloses thermal treatments combined with the ultrafiltration of a liquid dairy base to produce a concentrated dairy product having greater than about 9 percent protein (generally about 9 to about 15 percent protein), about 0.3 to about 17 percent fat (generally about 8 to about 8.5 percent fat), and less than about 1 percent lactose.
The process of Cale, however, discloses that all the protein and fat in the final concentrated beverage are supplied directly from the starting liquid dairy base and, therefore, the amounts in the final beverage are also constrained by the composition of the starting dairy base and the particular concentration process employed. In other words, if higher amounts protein or fat are desired in a final beverage obtained from Cale's process, then the other of the protein or fat is also increased by a corresponding amount because each component is only supplied from the same starting dairy base and, therefore, subjected to the same concentration steps. The process of Cale, therefore, will generally not permit a concentrated dairy beverage having increases in one of protein or fat and, at the same time, decreases in the other of protein or fat.